Conventionally, a die configured to extrude a molten resin into a strand is widely used to, for example, granulate the resin. A die of this type generally has a plurality of nozzle-like orifices. A molten resin supplied from an extrusion machine is extruded from the orifices into strands. When manufacturing (granulating) resin pellets, the resin extruded into a strand is cut to a predetermined length by a cutter blade.
When the nozzle-like orifice continuously extrudes a resin, a very small quantity of resin adheres to the edge of the orifice. The resin in the small quantity that adheres to the orifice edge is metaphorically called “die drool”. The die drool accumulates and increases in amount with the lapse of time. The die drool also deteriorates and discolors due to heat or progress of oxidation.
The uncontrolled die drool accumulates and increases in amount and peels off the orifice edges at a certain point of time. The die drool is then carried together with the extruded resin strands and mixed into granulated resin pellets as foreign substances. The die drool (foreign substances) has an outer appearance (color and shape) and physical properties different from those of a normally granulated resin. For this reason, if large die drool is mixed in the resin pellets, the outer appearance and physical properties of a molded form formed from the pellets are impaired.
There has been a proposal to suppress die drool generation and contamination of a product (pellets) with generated die drool (foreign substances). For example, PTL 1 discloses an extrusion machine which suppresses generation of die drool (foreign substances) as an independent solid or contamination by them by blowing a gas to the outer periphery (strand surface) of the tip of each orifice to blow the die drool off or by making the resin adhered to the orifice edges, which is still small in amount and has not yet so largely changed the properties, adhere to the surface of the molten resin (strands) so as to disperse and dilute it.